The present invention relates to spatial light modulators and particularly to reflective spatial light modulators used in projection display systems.
Reflective spatial light modulators (SLMs) are small structures typically fabricated on a semiconductor wafer using techniques such as optical lithography, doping, metal sputtering, oxide deposition, and plasma etching, which have been developed for the fabrication of integrated circuits.
Two types of reflective SLMs include micromirror devices and reflective liquid crystal on silicon (LCD) devices. These devices use digital image data to modulate a beam of light by selectively reflecting portions of the beam of light on to a display screen.
In these devices the precision of the reflection angle is critical for good optical efficiency. It is also critical that unwanted light not be reflected to the image where it would raise the black level and lower the image contrast. Thereby, a critical aspect in fabricating these devices is the smoothness of the reflective surface. For example, any stray light coming from the black areas of the image that gets into the projected image degrades the system contrast ratio. As a result, it is desirable to have extremely smooth reflective surfaces.
What is needed is a method to improve the reflectivity of a reflective spatial light modulator.
The present invention discloses a method for enhancing the optical performance of a reflective spatial light modulator by micro-planarizing surfaces within the SLM, including the reflective surface of each pixel and, in the case of micromirrors, any landing surfaces that have an effect on the tilt angle of the micromirror.
The present invention inserts a gas-cluster-ion-beam bombardment at one or more steps in the process. This process improvement has shown to improve the surface smoothness from xcexc=10, "sgr"=8 to xcexc= less than 3, "sgr"=2.
By improving the smoothness of the reflective surfaces in these reflective SLMs, which are primarily used in projection displays, the brightness and constant ratio of the projectors can be significantly enhanced.